The present invention relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a pulse width modulated downhole flow control.
Typical downhole flow control devices are designed for permitting substantially continuous flow rates therethrough. For example, a sliding sleeve valve may be set at open and closed positions to permit respective maximum and minimum flow rates through the valve. A downhole choke may be set at a position between fully open and fully closed to permit a substantially continuous flow rate (provided certain parameters, such as fluid density, temperature, etc., do not change) which is between respective maximum and minimum flow rates.
However, it may be beneficial in some circumstances (e.g., to enhance productivity, sweep, etc.) to be able to control or change the flow rate through a downhole flow control device. This cannot conveniently be accomplished using typical flow control devices, because they generally require intervention into the well, application of pressure via long restrictive control lines and/or operation of complex control systems, etc. Therefore, improvements are needed in downhole flow control devices to permit variable control of flow rates through the devices.
An electrically powered flow control device could be suitable for controlling flow rates. The most common methods of supplying electrical power to well tools are use of batteries and electrical lines extending to a remote location, such as the earth's surface.
Unfortunately, some batteries cannot operate for an extended period of time at downhole temperatures, and those that can must still be replaced periodically. Electrical lines extending for long distances can interfere with flow or access if they are positioned within a tubing string, and they can be damaged if they are positioned inside or outside of the tubing string.
Therefore, it may be seen that it would be very beneficial to be able to generate electrical power downhole, e.g., in relatively close proximity to a flow control device which consumes the electrical power. This would preferably eliminate the need for batteries, or at least provide a means of charging the batteries downhole, and would preferably eliminate the need for transmitting electrical power over long distances.